A brake booster having attachment tubes is discussed, for example, in EP 2,058,195.
FIG. 4, which is based on FIG. 2C of EP 2,058,195, shows the bypass tube of a vacuum brake booster according to the state of the art. The references found in FIG. 2C of EP 2,058,195 are used here as a reminder of the state of the art.
Screw bypass tube 222 is attached to back 213 by its fold 240, which forms a support surface. Cover 215 is attached, near the other end of the bypass tube, by washer 230, which presses against an axial stop in the form of a fold realized at this location of bypass tube 222. Beyond cover 215, the bypass tube has a threaded exterior zone accommodating a sleeve enlarging the diameter and traversing lug 203 of the master cylinder.
The sleeve has an exterior thread to accommodate nut 234, securing lug 203 to the sleeve.
The brake booster is attached by screw 220, whose head, of reduced diameter, 222, presses against extremity 232 of the sleeve. Threaded portion 236 crosses the bulkhead of the engine compartment for attachment by a nut, not shown.
This assembly uses frontal washer 230 to support the stress of the torque associated with attaching the master cylinder with a shoulder or fold realized on tube 222 to constitute the washer support. Under these conditions, bushing 232 must be used on the portion of tube 222 outside the housing to increase the diameter of the threads for attachment of lug 203 of the master cylinder with nut 234. This increase in diameter is necessary so the master cylinder can be removed without removing the pneumatic vacuum brake booster by accessing screw head 221 without removing it.